There are many situations in which it is necessary and/or desirable to determine the characteristics and quantity of foreign matter which is entrained, in a liquid system. Such a determination is particularly difficult when flowing liquid-liquid or liquid-gas systems are involved, especially those which are subjected to turbulence, since the foreign matter, liquid or gas, if immiscible in the flowing liquid stream, is usually emulsified, suspended or otherwise dispersed in the form of droplets of varying sizes. Sufficient characterization of such dispersed impurities thus requires a measurement of droplet number distribution, droplet size distribution, droplet composition distribution, as well as other parameters such as droplet densities, etc. Heretofore, such measurements have not been possible on a commercial scale.
One area particularly sorely in need of such measurement capability is offshore oil well technology. During the pumping of oil from sea-based platforms, a quantity of brine is unavoidably obtained along with the desired oil. This brine is referred to as "produced water". Because of its presence, the problem exists to remove the water from the oil generally by gravity separation or flotation.
In turn, such separation procedures make very desirable techniques for determining the quality of the oil/water separation on as quantitative a basis as possible. Since the oil/water mixture is blown through a small orifice during the pumping procedure, and since high velocities are required in the pipelines to maximize throughput, the oil is very greatly dispersed in the water by the high shear forces which are created. Accordingly, this quantifying of the quality of the oil/water separation becomes a problem of characterizing the oil droplet distribution within the produced water.
The problem is exacerbated by the existence of gas bubbles in the oil/water emulsion. In addition, solid matter is often also entrained. Accordingly, it is not only necessary to characterize the properties of the oil droplets in the flowing water, but it is also necessary to distinguish such droplets from similarly sized and shaped gas bubbles and other matter.
The characterization of the oil distribution within the water is further complicated by the fact that the flowing liquid stream is generally under relatively high pressure which may vary within a wide range, e.g., about 1 to 100 psig. Accordingly, any measurement system must be capable of sampling the liquid stream within this entire range, preferably on a continuous basis. Furthermore, in order to ensure reliability, the sampling operation itself must not perturb the characteristics of the oil droplets which are being measured.